A conventional secondary battery structure as shown in FIG. 1A includes a jar body 100, end covers 102, battery terminals 104 penetrating the end covers 102, and screw nuts 106. As indicated in FIG. 1B, the conductive stacked structure in the jar body 100 often refers to a battery unit 114 constituted by a jelly-roll 108, a central rod 110, and conductive tabs 112. To ensure that the conductive tabs 112 are in contact with the battery terminals 104, an individual conductive terminal 116 is respectively configured at two ends of the central rod 110. Each individual conductive terminal 116 has a protrusion 118 and a fixing pin 120, the battery terminal 104 is screwed onto the protrusion 118, and the fixing pin 120 is fixed at the central rod 110. Besides, a circular hole 122 corresponding to the protrusion 118 is configured at the bottom of the battery terminal 104, and a rectangular hole 124 for correspondingly fixing the fixing pin 120 is configured at the two ends of the central rod 110, respectively. During assembly of the secondary battery structure, the protrusion 118 passes through the circular holes 126 of the conductive tabs 112, the fixing pins 120 are placed into the rectangular holes 124, and the tops of the battery terminals 104 pass through the screw nuts 106 and the end covers 102 depicted in FIG. 1A, so as to screw the end covers 102 and the conductive tabs 112 together.
The construction and configuration described above lead to dimension errors of the conductive stacked structure in the jar body 100, and therefore the fixing pins 120 are partially exposed and are not completely inserted into the central rod 110 in most cases, as indicated in FIG. 1C, which is a schematic cross-sectional view illustrating a portion of the secondary battery structure after assembly. Due to the dimension errors, a gap that allows the jelly-roll 108 to move is formed between the jelly-roll 108 and the end covers 102. When an external force is applied to the secondary battery structure, e.g., when the secondary battery structure is vibrated or hit, the battery unit (e.g., the jelly-roll 108) in the jar body 100 moves up and down because of gravity or the inertial force. Thereby, the jellyroll-shaped battery cell hits the conductive stacked structure and is damaged, which may pose a safety hazard to users. Furthermore, when the end covers 102 and the conductive tabs 112 are screwed together, metallic fragments are likely to fall into the jar body 100, which raises issues of electrical properties and safety.